1. Field of the Invention
The present invention relates to a tape amount displaying apparatus. More particularly, the present invention relates to an improvement of a display apparatus for displaying an amount of a tape, such as a used amount of a magnetic tape or a remaining amount of the magnetic tape in a tape-recorder.
2. Description of the Prior Art
A conventional tape amount displaying apparatus in a tape-recorder has been adapted such that a rotational period of a reel is sequentially measured and the measured result is multiplied by a tape travelling speed so that the length of an outermost periphery of the tape wound in the reel is evaluated, and then the tape amount is calculated from the length of the outermost periphery of the tape and displayed. According to such conventional system, a remaining amount of the tape can be precisely displayed only if a tape travelling speed is constant in recording or reproducing, for example and constant rotational frequency can be measured. However, in fast-forwarding or rewinding a tape, a tape travelling speed changes depending on the amount of tape on a supply reel or a takeup reel and hence a constant rotational period of a reel can not be measured. In such a case, there is a disadvantage, that the tape amount can not be calculated and displayed.
In order to overcome such a disadvantage, the following approach can be considered. Particularly, there is provided a roller always in contact with a tape and an apparatus for measuring the rotational speed of the roller, so that a varying tape travelling speed is evaluated. Then, an average tape travelling speed in a predetermined time period is evaluated based on the varying tape travelling speed and the rotational frequency of the reel, so that the tape amount can be calculated. However, such an approach has a new problem in that the display apparatus thus structured becomes complicated and expensive.